Neutralizing organic materials



March 1944. (5. DE w. MILES ETAL NEUTRALIZING ORGANIC MATERIALS Filed July 11, 1942 2 Sheets-Sheet 1 STORAGE MERCURY MERCURY (PURE) POTAS$IUM CHLORIDE CALOMEL IIIHJIMIAJJJ GlLBERT DE WAYNE MILES CONRAD WILLIAM JAKQB JOSEPH HENRY PERCY March 28, 1 4- G. DE w. MILES ETAL NEUTRALIZING ORGANIC MATERIALS Filed July 11, 1942 2 Sheets-Sheet 2 COTTONSEED-SODA SOAP 32% MOISTURE SAT'D CALOMEL & ANTIMONY ELECTRODES lao'F.

"20m 3512 n ow Qu H. w. o m m E M F IN MILLIVOLTS .Fzvezflbra GILBERT D'E WAYNE MILES CONRAD WlLLlAM JAKOB JOSEPH HENRY. PERCY Patented Mar. 28, 1944 I I I 2,345,465 nnormmrzmo. ORGANIC MATERIALS Gilbert De Wayne Miles, New York, N. Y., Conrad William Jakob, Secaucus. N. J., and Joseph Henry Percy, New York, N. Y., assignors to Colgate-Palmolive-Peet Company, Jersey City,

N. J., a corporation of Delaware Application July 11, 1942, Serial No. 450,646

1'! Claims.

The present invention relates to a novel method for determining the free acidity or free alkalinity of fluid salt compositions and, more particularly, to a new method for controlling the free alkali content of soaps and soap products.

A small amount of free alkali in soap is a desirable constituent in order to prevent rancidity.

When manufacturing soap from oils and fats by saponification with alkali, it has always been the practice to leave a small proportion of free alkali in the finished product. This proportion has varied from about 0.05% in fine toilet soaps to about 0.4% in laundry soaps.

In manufacturing soap by the kettle method, any desired proportion of free alkali may be easily attained. Glycerine produced in the saponification of oils and/or fats is salted out, and excess alkali is removed with the brine solution which settles to the bottom. The aqueous extraction may be continued until the content of free alkali has reached a predetermined amount. The free alkalinity is determined by titration after solution in alcohol and, when working with large batches, there is no dimculty in running the few titrations necessary. Because of this ease of determining and controlling the soap composition when manufacturing by the kettle" process, the soap industry has had no problem in this respect until the introduction of various methods of continuous saponification.

When manufacturing soap by continuous saponiflcation of oils and/or fats vor by continuous neutralization of fatty acids, a determination of alkali content by this method proved very cumbersome and expensive, as it necessitated continuous withdrawal of samples and repeated titrations and required the constant services of an operator in order to permit control of the con tinuous operation with a sufficiently short time lag. Moreover, according to most continuous processes, an aqueous extraction is not employed, but glycerine, if present, and water or other solvent, if removed at all, are removed by vaporization, distillation, flashing or the like, so that any free alkali present remains in the soap. It therefore becomes necessary to use only an accurately proportioned amount of alkali for a given quantity of fatty acid or oil, but, even with this precaution, it is desirable for the operator to be able continuously to determine the free alkali content and accurately to control the soap composition.

Until the advent of the present invention, the soap industry, so far as is known, has had no successful method for continuously determining or accurately controlling the free alkali content of soaps on a practical and industrial scale.

It is an object of the present invention to provide a novel method for determining the free acidity or free alkalinity of fluid salt compositions. having less than 60% water, especially compositions of salts of a weak acid.

It is another object of the invention to provide a new method for measuring the free alkali or free fatty acid content of soap.

It is also an object of this invention to provide a method for accurately controlling the composition of soap made by continuous processes.

Other objects and advantages of the invention will be apparent from the following description, taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a diagrammatic representation of an apparatus assembly in accordance with the present invention;

Fig. 2 illustrates a detailed diagram of an electrical circuit for measuring the potential between a fluid hydrated soap and 'anelectrode of special character;

1 Fig. 3 depicts one type of reference electrode which may be employed in this invention; and

Fig. 4 shows a curve illustrative of determinations obtained with a typical hydrated soap.

It has been found that the free acidity or free alkalinity of a fluid hydrated soap is a function of the potential between a test electrode of special character and the soap, and, according to this invention, a measure of the free acidity or free alkalinity of the soap can be obtained by measuring said potential, even though this result is not measurable in terms of pH. A potential characteristic of a particular free alkali content can then be determined for a soap of given fatty acid composition and hydration at a specified temperature, and variations from this potential can be indicated and/or employed to control the amount or proportion of alkali admitted to the saponifying unit.

The potential between the test electrode and the fluid hydrated soap is a result of the reaction between the electrode and the constituents of the soap in contact with it. As there is no convenient method known for directly measuring this potential, a reference electrode in a solution of known concentration in contact with the fluid hydrated soap to be tested is employed, and the potential between the two electrodes is measured. Given the potential between the reference electrode and the known solution, the potential between the test electrode and the soap is readily calculated.

The reference electrode may be a silver-silver oxide couple or may preferably be a calomel electrode of known type, containing mercury in cona glass electrode using special low-alkali glass, or

any other electrode which does not deteriorate under use and which shows little, if any, sodium ion error under the operating conditions. In its simplest form, the antimony electrode consists merely of a small casting of specially prepared antimony with an antimony oxide coating, one

end'of which is immersed in the fluid hydrated soap. In continuous operation, it is preferred that means. such as a soft rubber blade suitably mounted, be provided therewith for mechanically wiping the electrode at frequent intervals to sweep the electrode surface clean of soap. Because of the high viscosity characteristics of soa there is apt to be a lag due to failure of the soap flow to remove soap from the electrode surface, unless this precaution is observed.

The potential or voltage between the reference electrode and the test electrode is measured by a potentiometer. as will appear infra. and the known reference potential of the reference electrode is then subtracted therefrom to obtain the desired single electrode potential of the material under test. The potential of the calomel electrode varies with its temperature as well as with concentration of potassium chloride, being fixed for each particular set of conditions. When the measured voltage is diminished by the potential appropriate to the electrode used for reference, the remainder shows the single electrode potential of the test material, when both electrodes and test material are at the same temperature. The following description of an apparatus for controlling the free alkali content of a fluid hydrated soap is illustrative of a means for carryin out the process of the present invention, and it will be understood that the invention is not limited thereto. Referring to Fig. 1, reference character I designates a supply tank for holding fats. fatty oils and/or fatty acids, the outlet of the tank being connected through a conduit with a positive volumetric displacement pump 2 driven by a motor 3. A pipe from the pump leads into a saponification or neutralization contactor conduit 4. The outlet of an alkali supply tank '5 is connected through a conduit to a second volumetric displacement pump 8, which is driven by a motor I.

A conduit connected to the delivery end of the second pump 8 leads into the contactor conduit I, and means are provided for obtaining a turbulent mixing and reaction of the fatty oil or fatty acid with the alkali. Near the outlet end of the contactor conduit, a chamber 8 equipped with a reference electrode 9 and a test electrode Iii is provided, said electrodes being adapted for immersion in the material flowing through the conduit. The electrodes are connected to two poles on a potentiometer II. and the nature of the connection, as well as of the potentiometer circuit can be seen by reference to Fig. 2. The potentiometer is in turn connected with a threeposition relay l2 associated with an intermittent reversible motor H. The motor I3 is connected with the pump 2 and is adapted to control the .defiection of the galvanometer.

stroke of said pump. The amount or proportion of fatty acid delivered by the pump is thus controlled from the potentiometer.

Referring to Fig. 2, the potentiometer measuring circuit comprises a fixed, calibrated resistance wire ll of uniform resistance per unit length, stretched along a scale I! graduated in uniform divisions. A storage cell or battery it, preferably having a capacity of at least 20 ampere hours, is connected in series with the fixed resistance I 4 and with an adjustable resistance ll. The adjustable resistance ll can be varied by means of a contact l8, slidably mounted therealong. Connected with the potentiometer measuring circuit, there is a standardizing circuit, which comprises a standard cell It in series with a galvanometer 20 through one side of a two-way switch 2|, both the standard cell and the galvanometer being in series with a portion of the fixed resistance H. Completion of the stan'd-.

ardizing circuit through the fixed, calibrated resistance I4 is effected by means of a contact 22 which is slidably connected to the calibrated portion of the resistance wire at a point thereon.

The reference electrode 8 is connected to the side of the two-way switch 2| opposite the side to which the standard cell is connected, so that the reference electrode is thus adapted to be connected through the switch in series with the galvanometer 20 and a portion of the calibrated resistance H. The test electrode II is connected with a contact 23 which is slidably mounted upon the calibrated resistance It and which thus closes the test circuit. The galvanometer 2| 'is suitably connected to the relay l2 asbociated with the motor II, and means, not shown in the figures, are provided for increasing or decreasing the stroke of the fatty acid pump 2 according to the Such means may comprise any suitable device, such as provided with the "Micromax recorders. Means for electronic amplification may also be provided where the high resistance of the soap makes suchprovision desirable.

The test electrode may advantageously be a straight bar of antimony specially prepared with a uniform coating of antimony oxide. It is preferably encased so that only one end is in contact with the soap. A vertical rotatable rod 2| (see Fig. 1) is positioned in the chamber 8, passing upward through the bottom of the chamber to a point just below and slightly to one side of the end of the electrode, and upon the upper end of this rod is mounted a soft rubber arm 25 adapted to make wiping contact with the end of the electrode. Means, not shown, for rotating the rod 24 are provided.

The reference electrode is advantageously a saturated calomel electrode. Referring to Fig. 3,

a suitable type of calomel electrode is shown;

The electrode comprises a glass vessel 28 having a very small orifice 21 through its bottom, said orifice being filled by a permeable fibre plug 28. A narrow tube 29 closed at its lower end extends through the top of the vessel to a position near the bottom of the inside thereof, said tube being divided into two portions connected by a platinum wire 30, which extends from the upper portion of the narrow tube through the seal between said portions and into the lower portion of the tube. The tube has a small orifice 3| near its lower end, said orifice being filled by afibre plug 32. A layer of calomel is provided in the bottom of the tube 28, said "layer extending above the orifice 3|, and ,a pool of pure mercury lies above the calomel layer and immerses a portion of the platinum wire 30 which extends into the lower portion of the narrow tube 28. Filling the remainder of the glass vessel 28 not occupied by the tube 29, an aqueous solution saturated with potassium chloride is provided, and the flbre plugs 28 and 32am adapted to permit slow diffusion of this solution into the fluid hydrated soap into which the electrode 9 is immersed and into the layer of calomel at the bottom of tube 29, respectively. The upper portion of the narrow tube 29 is filled with technical mercury, and a wire dips into this mercury from above and is connected to the potentiometer as detailed supra.

The operation of this apparatus and of the method in which it is used is very simple and can be placed in the charge of even non-technical operators. Before operation is begun, the potentiometer is standardized by moving the switch 2| to close the standardizing circuit. The contact 22 is then moved along the resistance wire H (shown as a distance between point A and point B) until a point C is reached which is equivalent in divisions of the scale from point A to the number of millivolts of potential difference between the electrodes of the standard cell. The galvanometer ordinarily shows a deflection when this is done, and the contact I8 is then moved along the adjustable resistance l1 until the galvanometer shows no deflection. Under these conditions, the flxed resistance is calibrated so that each division of the scale represents one millivolt difference in potential.

At the beginning of the operation, fatty acids (for example) are pumped through pump 2 into the contactor conduit in confluence with a predetermined proportion of alkali delivered by pump 6. The two materials are turbulently mixed, and a hydrated soap is delivered from the contactor conduit outlet to the storage tanks. Switch 2| is thrown in the other direction to connect the reference electrode 9 and the test electrode III with the galvanometer and the calibrated resistance. The contact 23 is then slid along the resistance wire l4 until a point D is reached at which the galvanometer shows no deflection. The number of scale divisions corresponding to the distance from point A to point D is a measure of the potential difference between the reference and the test electrodes in millivolts, and, if desired. the potential between the test electrode and the hydrated soap can be determined by subtracting from this measured value the known value for the potential of the saturated calomel electrode at the particular temperature. Having found the potential between test electrode and soap, the free alkali content'corresponding thereto for the particular soap composition and hydration at the specified temperature may be readily found by reference to a curve, such as is shown at Fig. 4 and as will be discussed infra.

In controlling the free alkali content of a fluid hydrated soap having particular fatty acid composition and hydration, it is generally unnecessary to go through this calculation. Having predetermined by a series of tests and titrations the curve for the particular soap in abscissae of millivolts of potential difference between the test electrode and the known conber of millivolts corresponding to the desired alkali content on the curve. Having thus set the desired potential difference, any deflection of the galvanometer 20 indicates a departure from the desired alkali content for the soap. The stroke of pump 2 can then be changed to vary the amount of fatty acid delivered to the contactor conduit and thus to correct the free alkali content of the soap until the galvanometer shows no deflection. .The galvanometer is connected to the three-position relay l2 in such manner that deflection of the galvanometer to one side causes the motor ii to rotate in one direction, whereby the stroke of the pump 2 and the amount of fatty acid delivered thereby are increased, and deflection to the other side causes rotation of the motor l3 in the opposite direction with consequent shortening of the stroke of the pump and decrease in the amount of fatty acid delivered.

In preparing a curve for indicating the relation between the difference in potential of an antimony electrode and a saturated calomel electrode in fluid hydrated soap at a particular temperature and the percentage of free alkali in the soap, figured as NazO, the soap is made by any saponiflcation method desired, whether kettle boiling, continuous saponiflcation of glycerides or esters, continuous neutralization of fatty acids or the like. Thus, for example, preheated cottonseed oil fatty acids are pumped into con fiuence with a proportioned preheated aqueous solution of caustic soda, the solution being of such concentration as to provide a soap con taining about 32% moisture. An apparatus similar to that depicted at Fig. 1 may be employed, and temperatures are so maintained as to deliver soap from the contactor conduit at about 180 F. The potential between an antimony electrode and a saturated calomel electrode is measured by the method described, and, after the measurement is recorded, a small sample of the soap is withdrawn and titrated with phenolphthalein in alcoholic solution to find the percentage of free alkali as NazO. The measured potential in millivolts is then plotted against the free alkali percentage obtained by titration to give a point on the curve. The stroke of the pump which delivers the fatty acid is then changed by small amounts, the potential between the electrodes being measured after each change and a sample being withdrawn each time for titration. In this manner, a series of points on the curve is obtained, running from deficiencies in alkali (i. e., soap containing unreacted stant reference electrode and in ordinates of free shown at Fig. 4. Differences in hydration of the soap tend to change the shape of the curve, but it will be understood from the foregoing that, for any given soap composition and hydration at a particular temperature, the curve is fixed.

Referring to Fig. 4, it will be observed that 0.25% of free alkali figured as NazO in the cottonseed-soda soap curve plotted gives a potential between the antimony and the saturated calomel electrodes of about 840 millivolts. This figure is considerably higher than the electrode potential obtained with 0.25% NazO in water, which is about 695 millivolts. Moreover, it is a surprising feature of the invention that an antimony electrode can be employed in the present process, as it is well known that antimony electrodes are not generally adaptable for use in solutions containing high concentrations of sodium salts. This is particularly true when the potential rises to about 720 millivolts, and, in the present process, the potential may rise far beyond this E. M. F. without harm to the antimony electrode or substantial error in measurements therewith.

It will also be observed that, according to the curve of Fig. 4, free acidity in the soap has been represented as negative free alkalinity. This has been found convenient, so that comparable figures as percentage of Na2O may be used to exnitrogen-containing groups, acyloxy groups.

- alkoxy groups, ketonic groups, etc.

press either free acidity or free alkalinity. The

term free alkali as used herein is therefore intended also to include free acid.

The method herein described is applicable to fluid hydrated soaps containing up to about 60% moisture, which is just the range at which the prior art experienced its greatest difliculty, and especially to soaps having less than about 35% moisture. Soaps having up to about 60% moisture (say, less than about 35% moisture) have a discontinuous aqueous phase. Greater proportions of water than 60% give excessive hydrolysis of the soap, resulting in free alkali even when the soap is analytically on the acid side. The method is not limited to any particular temperature range, being applicable even at temperatures at which the soap is apparently solid. However, precaution must be taken to insure that the electrode surface is wet by the sample being tested.

Although the method herein described is particularly adaptable for controlling the free alkali content of soaps prepared by continuous saponification of glycerides or esters and/or by the continuous neutralization of fatty acids, it may also be applied to soaps made by batch or intermittent processes, such as in kettle boiling, and to other fluid compositions of salts of a weak acid having a discontinuous aqueous phase. This method is also applicable in the fleld of synthetic detergents, especially those of the type of salts of sulphated and/or sulphonated organic materials, including fatty oils, mineral oils,

and numerous other organic compounds and mixtures of compounds. These organic compounds, the salts of the sulphate or sulphonate derivatives of which may be prepared by hydrolysis and/or neutralization of sulphonic derivatives as aforesaid with an alkaline material, can be sulphonated by any ofseveral methods and may form any of several products, depending upon the method of sulphation or sulphonation employed, including sulphonates prepared by treatment of organic materials with sulphur dioxide and chlorine in the presence of actinic light and hydrolysis of the product, and, sulphonates prepared by treatment of organic bodies with sulphuryl chloride and an activating agent in the presence of actinic light and hydrolysis of the product. These organic sulphate and sulphonate salts may include watersoluble detergents, whether the organic radicals of the molecule are unsubstituted or contain substituents as halogens, halogenoids, hydroxyls,

The method of the invention is applicable, too, for controlling the neutralization of various detergent products, including creams and pastes. such as tooth pastes, hand pastes, shaving creams, cosmetic creams, superfatted soaps and the like. Similarly, although the present invention has one of its greatest applications in the detergents and soap-making arts, it will be appreciated that the same method of controlling free alkalinity or free acidity may be employed in the preparation of other compounds where a pH determination would be meaningless, as in the preparation of other materials in solvents other than water.

Thus, although the present invention has been described with respect to particular embodiments and examples, it will be appreciated by those skilled in the art that variations and modifications of the invention may be made and that various equivalents may be substituted therefor without departing from the true spirit of the in vention. For example, while the means for controlling the amount of fatty material or alkaline agent has been particularly described as comprising a means for shortening or lengthening the stroke of a pump'delivering such reactant, other control means, such as means for changing the speed of the pump or for regulating the temperature of fluids passing thereto to change the gravimetric amount delivered by a change in density or viscosity, may also be used. These and other variations and modifications are believed to be within the scope of the present specification and within the purview of the appended claims.

We claim:

1. A method of determining the free alkali con tent of a fluid salt composition which comprises measuring the potential between an electrode wet by a fluid composition of a salt of a weak acid having a discontinuous aqueous phase and a water content less than about 60% and a reference electrode in a known solution in contact with said fluid composition, and comparing said measured potential with predetermined values for potential between said electrodes in said fluid composition at substantially the same water content and in said known solution, respectively, cor responding to various values for free alkali content of said fluid composition.

2. A method of determining the free alkali content of a fluid salt composition which comprises measuring the potential between a suitable electrode wet by a fluid composition of a salt of a weak acid having a discontinuous aqueous phase and a given water content less than about 60% and at a given temperature and a reference electrode in a known solution in contact with said fluid composition and at substantially the same temperature, and comparing said measured potential with predetermined valuesfor free alkali content corresponding to various potentials between said electrodes in said fluid composition at substantially the same water content and temperature and in said known solution at substantially the same temperature, respectively.

3. A method of determining the free alkali content in a fluid soap having less than about 60% water which comprises measurin the potential between an electrode wet by said soap and a reference electrode in a known solution in contact with said soap, and comparing said measured potential with predetermined values for potential between said electrodes in said soap and in said known solution, respectively, corresponding to various values for free alkali content of said soap.

4. A method of determining the free alkali contentin a fluid soap having less than about 35% water which comprises measuring the potential between a suitable electrode wet by a fluid hydrated soap of given water content less than about 35% and at a given temperature and a reference electrode in a known solution in contact with said soap and at substantially the same temperature, and comparing said' measured potential with predetermined values for potential between said electrodes in said soap at substantially the same water content and .temperature and in said known solution at substantially the same temperature, respectively, said values for potential being predetermined for various known contents of alkali in said soap.

5. A method of determining the free alkali content in a fluid soap having less than about 60% water which comprises measuring the potential between an antimony electrode wet by a fluid soap. or water content less than about 60% and a calomel electrode in said soap, and comparing said measured potential with predetermined values for potential between said electrodes in said soap at various contents of alkali of said soap, whereby an alkali content corresponding to said measured potential can be observed.

6. A method of determining the free'alkali content in afluid soap having less than about 35% water which comprises measuring the potential between an antimony electrode wet by a fluid hydrated soap of water content less than about 35% and at a given temperature and a saturated calomel electrode in said soap, and comparing said measured potential with predetermined values for potential between said electrodes in said soap at substantially the same temperature and at various contents of alkali of said soap, whereby an alkali content corresponding to said measured potential can be observed.

7. A method of controlling the free alkali content of a fluid salt composition which comprises predetermining the potential between a suitable electrode wet by a fluid composition sample of a salt of a weak acid having a discontinuous aqueous phase and a water content less than about 60% and of desired free alkali content and a reference electrode in 'a known solution in contact with said fluid composition sample, preadjusting a potentiometer circuit to show a substantially zero galvanometer deflection when placed across said predetermined potential, measuring on said potentiometer circuit the potential between said suitable electrode wet by a fluid composition of said salt having substantially the same water content as said fluid composition sample and of undetermined free alkali content and said reference electrode in said known solution in contact with the fluid composition, whereby variations from said desired free alkali content cause deflections of the galvanometer, and regulating the proportion of constituents in said fluid salt composition to maintain a substantially zero galvanometer deflection.

8. A method of providing a fluid salt composition of uniform free alkali content which comprises measuring the potential between an eleccomposition to maintain said potential substantially constant.

9. A method or controlling the free alkali content in a fluid soap having less than about 60% water which comprises predetermining the potential between a test electrode wet by a fluid soap sample having less than about 60% water and or desired alkali content and a reference electrode in a known solution in contact with said soap sample, preadjusting apotentiometer circuit to show a substantially zero galvanometer deflection when placed across a potential equivalent to said predetermined potential, measuring on said potentiometer circuit the potential between said test electrode wet by a fluid soap of substantially the same composition and hydration as said soap sample and of undetermined free alkali content and said reference electrode in said known solution in contact with the fluid soap whereby variations from said desired free alkali content cause deflections of the galvanometer, and regulating the proportion of constituents in said fluid soap to maintain a substantially zero galvanometer deflection.

10. A method of controlling the rreegalkali content in a fluid soap having less than about 35% water which comprises predetermming the potential between a test electrode wet by a fluid hydrated soap sample at a given temperature having less than about 35% water and of desired iree alkali content and a reference electrode in a known solution in contact with said soap sample and at substantially the same temperature, preaojusting the potentiometer circuit to show a substantially zero galvanometer deflection when measuring said predetermined poten tial, measuring on said potentiometer circuit the potential between said test electrode wet by a fluid hydrated soap of substantially the same composition and hydration as said soap sample and at substantially the same temperature and of undetermined free alkali content and said reference electrode in said known solution in contact with the fluid soap and at substantially the same temperature whereby variations from said desired free alkali content cause deflections oi the galvanometer, and adjusting the free alkali content of said fluid soap by an amountsuificient to maintain a substantially zero galvanometer deflection.

11. A method of controlling the free alkali content in a fluid soap having less than about 35% water which comprises predetermining the potential between an antimony electrode wet by a fluid hydrated soap sample at a given temperature having less than about 35% water and of desired free alkali content and a saturated calomel electrode in said soap sample, preadjusting a potentiometer circuit to show a substantially zero galvanometer deflection when measuring a potential equivalent to said predetermined potential, measuring on said potentiometer circuit the potential between an antimony electrode wet by a fluid hydrated soap of substantially the same composition and hydration as said soap sample and at substantially the same temperature and of undetermined free alkali content and a saturated calomel electrode in said fluid soap whereby variations from said desired free alkali content cause deflections of the galvanometer, and adjusting the free alkali content of said fluid soap by an amount sumc'lent to maintain a substantially zero galvanometer deflection.

12. A method of providing a fluid soap of uniform free alkali content which comprises measuring the potential between a suitable electrode wet by a fluid soap having less than about 60% water and a reference electrode in a known solution in contact with said soap, and regulating the proportion of free alkali in said fluid soap to maintain the potential substantially constant.

13. In a continuous process of preparing soap having less than about 35% water and of desired free alkali content by admixture of fatty material with an alkaline agent, the improvement which comprises predetermining the potential between a test electrode wet by a fluid hydrated soap sample having. less than about 35% water and of desired free alkali content and a reference electrode in a known solution in contact with said soap sample, preadjusting a potentiometer circuit to show a substantially zero galvanometer deflection when measuring a potential equivalent to said predetermined potential, measuring on said potentiometer circuit the potential between said test electrode wet by a fluid hydrated soap of substantially the same composition and hydration as said soap sample and of undetermined free alkali content and said reference electrode in said known solution in contact with the fluid soap whereby variations from said desired free alkali content cause deflections of the galvanometer, and proportioning the amount of fatty material to the amount of alkaline agent to maintain a substantially zero galvanometer deflection.

14. In a continuous process of preparing soap having less than about 60% water and of desired free alkali content by admixture of fatty material with an alkaline agent, the improvement which comprises predetermining the potential between an antimony electrode wet by a fluid soap sample at a given temperature having less than about 60% water and of desired free alkali content and a saturated calomel electrode in said soap sample, preadjusting a potentiometer circuit to show a substantially zero galvanometer deflection when measuring a potential equivalent to said predetermined potential, measuring on said potentiometer circuit the potential between an antimony electrode wet by a fluid soap of substantially the same composition and hydration as said soap sample and at substantially the same temperature and of undetermined free alkali content and a saturated calomel electrode in said fluid soap whereby variations from said desired free alkali content cause deflection of the galvanometer, and proportioning the amount of fatty material to the amount 'of alkaline agent to maintain a substantially zero galvanometer deflection.

15. In a continuous process of preparing soap having less than about 60% water and of desired free alkali content by admixture of fatty material with an alkaline agent, the improvement which comprises predetermining the P tential between a test electrode wet by a fluid soap sample having less than about 60% water and of desired free alkali content and a reference electrode in a known solution in contact with said soap sample, preadjusting a potentiometer circuit to show a substantially zero galvanometer deflection when measuring a potential equivalent to said predetermined potential, measuring on said potentiometer circuit the potential between said test electrode wet by a fluid soap of substantially the same composition and hydration as said soap sample and of undetermined free alkali content and said reference electrode in said known solution in contact with the fluid soap whereby variations from said desired .free alkali content cause deflections of the galvanometer, and adjusting the amount of fatty material admixed with said alkaline agent to maintain a substantially zero galvanometer deflection.

16. In a continuous process of preparing soap having less than about 35% water and of desired free alkali content by admixture of fatty material with an alkaline agent, the improvement which comprises predetermining the potential between an antimony electrode wet by a fluid hydrated soap sample at a given temperature having less than about 35% water and of desired free alkali content and a saturated calomel electrode in said soap sample, preadjusting a potentiometer circuit to show a substantially zero gal vanometer deflection when measuring a potential' equivalent to said predetermined potential, measuring on said potentiometer circuit the potential between an antimony electrode wet by a fluid hydrated soap of substantially the same composition and hydration as said soap sample and at substantially the same temperature and of undetermined free alkali content and a saturated calomel electrode in said fluid soap whereby variations from said desired free alkali content cause deflections of the galvanometer, and automatically controlling by said deflection the amount of fatty material admixed with said alkaline agent to maintain a substantially zero galvanometer deflection.

17. In a continuous process of preparing soap having less than about 35% water and of uniform free alkali content by admixture of fatty material with an alkaline agent, the improvement which comprises measuring on a potentiometer circuit the potential between an antimony electrode wet by a fluid hydrated soap of water content less than about 35% and a saturated calomel electrode in said soap, adjusting the potentiometer circuit to show a substantially zero galvanometer deflection at said measured potential whereby variations in the free alkali content of the soap cause deflections in the galvanometer, and automaticany controlling by said deflections the proportion of fatty material admixed with said alkaline agent to maintain a substantially zero galvanometer deflection.

GILBERT DE WAYNE MILES. CONRAD WILLIAM JAKOB. JOSEPH HENRY PERCY. 

